DIV. n 



ANGIOSPERMAE 



721 



by suppression of stamens or carpels, are unisexual. Male flowers, with numerous 

 stamens and sterile carpels ; female flowers, with staminodes and numerous free 

 carpels inserted. on the convex floral receptacle (Fig. 794). Leaves in Hutomus, 

 linear, channelled, and triangular in cross-section ; in Alisma and Sagittaria, 

 long-stalked with spoon-shaped and sagittate leaf-blades respectively. Individuals 

 of both genera growing in deep flowing water have long ribbon - shaped leaves, 

 similar to those that appear as a transition type in germination ; such plants do 

 not flower. 



Family 2. Potamogetonaceae. Many species of Potamogeton are distributed 

 over the earth in standing or flowing water. Leaves usually submerged, with a 

 long sheath, slit on one side, formed from the axillary stipules. P. natans, 

 the common Pond-weed (Fig. 795), at the time of flowering has usually only float- 

 ing leaves, the cylindrical, submerged water-leaves having disappeared by then/ 

 Ruppia maritime/, and Zanichellia palustris grow in brackish water. Zostera 

 marina, Grass-wrack, occurs commonly on all north temperate coasts and is used 

 for stuffing cushions. 



Family 3. Hydrocharitaceae. Hydrocharis morsus ranae and Stratiotes aloides 

 are floating plants occurring in Britain, which are vegetatively propagated by 

 runners ; they pass the winter at the bottom of the water, in some cases as special 

 winter buds, and grow up again in the spring. Flowers dioecious ; entomophilous. 

 The male flower has several trimerous whorls of stamens ; the female flower 

 possesses staminodes and two trimerous whorls of carpels. Vallisneria spiralis, a 

 fresh -water plant of the tropics ex- 

 tending to the Italian lakes. Elodea 

 canadensis, the Canadian water -weed 

 (hydrophilous, cf. p. 553). 



Order 2. Liliiflorae 



Flowers actinomorphic, com- 

 posed of five whorls, with superior 

 or inferior ovary. Both whorls of 

 the perianth developed alike (Fig. 

 792). Only in the Iridaceae is 

 one whorl of the androecium sup- 

 pressed. The gynaeceum varies 

 in position, but it is always formed 

 of three carpels and in most cases 

 has a trilocular ovary. 



Family 1. Juncaceae. Plants of 

 grass-like habit. Flower of complete 

 Liliaceous type ; with scaly perianth. 

 Wind-pollination. Pollen grains united 

 in tetrads. Ovary superior, uni- or tri- 

 locular, bearing three long papillose stigmas. Endosperm floury. Fruit a capsule. 

 Distributed in the temperate zones of both hemispheres. 



Numerous species of Juncus (Rush) occur in our flora, in marshy ground ; the 

 leaves are cylindrical and have large intercellular spaces. The clusters of small 

 anemophilous flowers (Fig. 796) are borne on the end of a shoot, but are often dis- 

 placed to the side by the bract which continues the line of the axis. Fruits with 



3A 



FIG. 796. Juncus lamprocarpus. a, Part of an in- 

 florescence : single flower (&) and gynaeceum 

 (c) magnified. 



